1. Field of the Invention
The present invention relates generally to charge-coupled devices, and more specifically to a method for improving the speed of operation of charge-coupled devices.
2. Description of the Related Art
For input devices such as digital cameras for personal computers, scan conversion from the interlace to noninterlace format is necessary since most of these devices are implemented with components used in the standard television systems, whereas the computers are noninterlace-format devices. In order to eliminate the need for scan conversion, the noninterlaced (progressive) scan format is increasingly adopted by current CCD imaging devices.
Japanese Laid-Open Patent Specification Hei-4-72762 describes a progressive-scan CCD imaging device using three-phase clock pulses for driving three electrodes of each cell for shifting charge packets along vertical shift registers (vertical CCDs) to a horizontal CCD. However, due to the large difference between the time constants of these electrodes, charge packets suffer undesirable effects such as distortion and delays. Therefore, the operating speed of the vertical CCDs is limited, resulting in a low charge transfer efficiency.